Neural delay in the ascending auditory pathway

Evoked responses from the cochlea and cochlear nucleus in the rat were studied using two types of stimuli: (1) bursts of tones or noise, and (2) continuous tones or noise that were amplitude modulated with pseudorandom noise. While the responses to the first type of stimuli were averaged only in the conventional way, the responses to the continuous and amplitude modulated sounds were averaged over one period of the pseudorandom noise. This average was then cross correlated with one period of the noise. The morphology of these cross correlation functions was in many ways similar to the response to transient sounds. Recordings from the round window of the cochlea and the cochlear nucleus showed that the latencies of these peaks in the responses to tone bursts and those of the cross correlation functions obtained from the continuous tones modulated with pseudorandom noise were similar. However, the latencies of the peaks in the cross correlation functions were slightly shorter and showed less dependency on the stimulus intensity than did the peaks in the responses to tone bursts. When the responses to noise bursts and the responses to noise that was amplitude modulated were compared, it was found that the latencies of the peaks in the cross correlation functions were nearly independent of the stimulus intensity. However, the peaks in the averaged responses to noise bursts showed a decrease in latency with increasing sound intensity.